Relative contributions of adiposity and muscularity to physical function in community-dwelling older adults

Objective: To determine the relative contributions of adiposity and muscularity to multi‐dimensional performance‐based and perceived physical function in older adults living independently. Methods and Procedures: Data from 109 women and men, aged 60 or older, with low serum dehydroepiandrosterone (DHEA) sulfate levels were included in this cross‐sectional analysis of baseline measures from a single‐site, randomized, controlled trial of DHEA replacement therapy. Physical function was determined by means of performance on the 100‐point Continuous Scale‐Physical Functional Performance (CS‐PFP) test and by self‐reporting using the physical function subscale of the Medical Outcomes Short Form‐36 (SF36_PF). Body composition was measured by dual‐energy X‐ray absorptiometry (DXA). Linear regression analyses were used to determine the contributions of body mass index (BMI; kg body mass/m²), fat index (FI; kg fat/m²), and appendicular skeletal muscle index (ASMI; kg muscle/m²) to the CS‐PFP and SF36_PF scores, adjusted for age and sex. Results: Age‐adjusted regression analyses indicated that FI, but not ASMI, was a significant (P < 0.001) determinant of CS‐PFP (R ² = 0.54) and SF36_PF (R ² = 0.37). When adjusted for age and sex, BMI was nearly as good a predictor of CS‐PFP (R ² = 0.50) and SF36_PF (R ² = 0.34) as FI. Discussion: Adiposity was a stronger predictor of measured and self‐reported physical function than was muscularity in older adults living independently. BMI, adjusted for sex, is a reasonable substitute for adiposity in the prediction of physical function.